The present invention generally relates to a method for producing an optical fiber of halide glass. More specifically, the present invention relates to a method for producing an infrared transmissive fiber of heavy metal fluoride glass.
Optical fibers are utilized for the transmission of communications over a distance. It has been suggested that infrared transmissive optical fibers of heavy metal fluoride glass, for example, based on barium fluorozirconate (BaF.sub.2 ZrS.sub.4) or beryllium fluoride may form the next generation of ultra-low-attenuation optical fibers for the transmission of communications over long distances. See, D.C. Transmission Conference on Optical Fiber Communication, Atlanta, 1986, reported in Technical Digest, pages 20-21.
Although there is a potential for heavy metal fluoride glass to form the next generation of infrared transmissive optical fibers, some of the properties of halide glass and requirements for optical fibers do not coincide. For example, the fiber must exhibit sufficient strength for practical applications as an optical fiber. However, this is opposed by the tendency of halide glasses manufactured from fluorides, chlorides, bromides, or iodides, to react at room temperature, or at least at fiber-drawing temperature, causing the absorption of hydroxyl groups from steam (water) and emission of gaseous hydrogen halide. This reaction has a deteriorating effect on the resultant strength of the fiber and likewise, can also increase the attenuation of the resultant optical fibers. These halide glasses are extremely reactive with water and even a nominally dry gas atmosphere is not sufficient for the production of fibers. Indeed, even an atmosphere having a water content of only approximately 1 to about 10 parts per million is not sufficiently dry for the production of halide glass fibers having an OH-free surface and, thus, good strength and not too thin.
Accordingly, there is a need for an improved method for producing optical fibers from halide glass, and specifically, an improved method for producing infrared transmissive fibers of heavy metal fluoride glasses.